A typical wireless communication system includes a number of base stations each radiating to provide coverage in which to serve wireless client devices (WCDs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped devices. In turn, each base station may sit as a node on a core access network that includes entities such as a network controller and a gateway system that provides connectivity with an external transport network such as the Internet. With this arrangement, a WCD within coverage of the system may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other WCDs served by the base station.
Such a system may operate in accordance with a particular air interface protocol, examples of which include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), BLUETOOTH, and others.
In accordance with the air interface protocol, a base station may provide service on one or more carriers, each spanning particular radio-frequency on which communications can flow wirelessly between the base station and WCDs. Such a carrier could be structured to provide a downlink for carrying communications from the base station to WCDs and an uplink for carrying communications from WCDs to the base station. For instance, the carrier could be frequency division duplex (FDD), with separate frequency ranges provided respectively for downlink and uplink communication, or time division duplex (TDD), with a single frequency range being time division multiplexed between downlink and uplink use.
Through modulation or other means on the carrier, the downlink and uplink could then be structured to define various channels for carrying communications between the base station and WCDs. For instance, the downlink could be structured to define one or more traffic channels for carrying bearer data from the base station to WCDs and one or more control channels for carrying control signaling from the base station to WCDs. And the uplink could define one or more traffic channels for carrying bearer data from WCDs to the base station and one or more control channels for carrying control signaling from WCDs to the base station.